Various commercial electrical devices contain internal components that must be shielded from the surrounding environment to prevent degradation. Additionally, some such devices also contain liquid components that must be incorporated in the device during manufacture but may evaporate afterwards unless the device is well sealed thereafter. Electrolytic capacitors and batteries are examples of such devices. Recently, new long life types of lithium non-aqueous batteries have become commercially available based on what is known as rocking chair or lithium ion electrochemistries. These batteries typically contain liquid organic electrolytes comprising solvent mixtures of esters, ethers, and the like. Difficulties exist, however, in adapting prior art filling methods with conventional container and terminal constructions when attempting to mass produce such batteries.
Often, commercial capacitors and batteries employ a deep drawn metal container that acts both as a container and as one of the electrical terminals for the device. The operating internal components of the device can be inserted into the container as an assembly, and a cover comprising an electrical feedthrough can then be employed to seal the device wherein the feedthrough acts as the other electrical terminal.
Conventional aqueous cylindrical batteries (eg. AA size alkaline batteries) employ a cylindrical metal container and metal cover construction wherein the cover is crimp sealed to the container using an insulating plastic gasket. Therefore, the cover itself acts as a feedthrough and terminal in this construction. Filling of the electrolyte is accomplished simply by dripping the liquid into the partly assembled battery comprising the container and internal electrical assembly. Generally, the electrolyte is added at a rate such that the liquid can be absorbed by the internal electrical assembly without ever creating a significant head. Otherwise, the liquid could wet the surfaces to be crimp sealed and thereby foul the seal itself. The appropriate electrical connection between the internal assembly and the cover may be made before or after the filling operation.
The aforementioned construction and filling method can be adopted successfully for non-aqueous lithium ion batteries. However, the typical electrolyte viscosity and the porous nature of the typical solid internal electrical assembly is such that the electrolyte must be added very slowly to avoid wetting the crimp seal surfaces. Even when the solid internal assembly is evacuated beforehand, this filling process can take of order of half an hour.
Prismatic batteries (ie. rectangular parallelepiped shape) are generally preferred for many applications but are somewhat more difficult to make. The manufacture of prismatic batteries can have many similarities to that of the aforementioned cylindrical batteries, but it is generally impossible to effect a satisfactory crimp seal using a rectangular cover. Thus, a weld is often employed to join cover and container in this case, and consequently the cover cannot be used as a second terminal (since it is electrically connected to the container via the weld). A feedthrough, remote from the welded cover periphery, is thus needed to act as a second terminal and is typically located and fabricated in the cover as a subassembly (ie. prior to wetting). Such feedthroughs can be a glass-metal seal type or a rivet seal type (such as the crimp seal design employing a rivet described in German Patent Application 3240806A1). The electrolyte filling operation thus can be performed as described previously, followed by a welding of the cover rather than a crimping.
It is undesirable however to perform high temperature welding operations in the presence of flammable non-aqueous liquids. Thus, filling of prismatic batteries with non-aqueous solvents is desirably performed after welding the cover in place. A means of dealing with this problem has been to construct pseudo-prismatic batteries having gentle curves which replace the right angle corners in the periphery of the cover (ie. rectangular covers with rounded corners). However, this construction sacrifices battery volume that is preferably used to the maximum in most applications.
Alternately, other means can be provided for filling after the joining of cover to container, such as that described in Canadian Patent No. 993,946 wherein a septum seal is effected in the cover as a subassembly (ie. the cover acts as a terminal and comprises a resealable septum as the fill port). Electrolyte is added via syringe through said septum after hermetically sealing the battery. Another approach is to provide a separate fill tube for addition of electrolyte after joining the cover and container. The fill tube can be severed and cold welded shut thereafter (as described in U.S. Pat. No. 3,809,580). However, such alternatives require additional parts thereby increasing complexity, external battery volume, cost, etc.